Reactive liquid polyamides derived from fatty polymer acids and various polyamines containing three or more amine groups are known. These products form linear condensation products which contain unreacted primary and secondary amine groups making them extremely useful as co-reactants with epoxy resins and phenol-formaldehyde resins. The utility of liquid reactive fatty polyamides is also well documented in the prior art.
To obtain liquid polyamides utilizing polyamines and polymeric fatty acids it is necessary to employ either a large excess of the polyamine or use a polyamine having very high amine functionality or both. In any event to obtain a liquid product with manageable viscosity the resulting polyamide will have a high amine value which is not desirable for all applications. For example, when one equivalent dimer acid is reacted with 2.4 equivalents diethylenetriamine the resulting polyamide has a very useful viscosity of about 13 poise at 75.degree. C. but the amine value is about 200-220. Reducing the amount of diethylenetriamine to about 1.6 equivalents lowers the amine value of the product to 90 to 95 but at the same time increases the viscosity so that to obtain the same viscosity it is necessary to heat the polyamide product to 150.degree.-160.degree. C. This complicates handling, requires more elaborate equipment for pumping and/or heating, and otherwise increases the processing costs.
While the presence of free amine groups in the polymer chain and pendant thereto is required for reactivity of these polyamide systems, it would be highly desirable if liquid reactive polyamides having reduced amine functionality were available. This feature would increase the utility of these products and make them particularly useful for blending with thermoplastic polyamide resins. Such blending procedures are finding widespread acceptability throughout the industry as a means of conveniently and economically altering the physical and chemical properties of thermoplastic polyamide materials. It is possible using such blending procedures to lower the softening point, reduce the melt viscosity and, in some cases, improve the adhesion characteristics of the material without detracting from the other desirable properties of the system. If liquid polyamides having reduced amine functionality were available it would increase the flexibility of such blending procedures and make it possible to obtain a greater variety of polyamide blends having useful properties.
It has now quite unexpectedly been found that liquid reactive polyamides having amine values less than 200 are obtainable by reacting polybasic acids and certain amine residues which will be more fully disclosed below. Surprisingly it has been found that typical products of this invention have manageable viscosities of 25 poise or below at 100.degree. C. or lower with amine values less than 140. This feature is highly desirable since 25 poise is considered to be about the upper limit of viscosity if a product is to be handled using gravity flow or slight pressurization. At higher viscosities more elaborate transfer means, e.g. gear pumps, are required or the product must be heated to a higher temperature to reduce the viscosity-- an approach which is undesirable because of the increased energy consumption and also because of the tendency of these materials to discolor when exposed to higher temperatures.